Aprilia MA MY 50 Workshop manual - Scootergrisen

Cylinder-head-piston unit
Using a bore gauge, check the diameter of the cylinder.
Compare your measurements with the table
below. If the measurements establish that the cylinder
is out of tolerance, you must replace the cylinder along
with the piston and rings (see Clearances Table).
Standard Wear limit
Cylinder
diameter “C”
39.99 to 40.01 mm
(1.574 to 1.575 in)
40.1 mm
(1.579 in)
Taper “T” * -- 0.05 mm
(0.0019 in)
Ovalization “R” ** -- 0.01 mm
(0.0004 in)
* where “T” is the result of the difference between T1 and T2.
** where “R” is the result of the difference between the two rightangle
measurements.
Piston - check
Remove the piston rings, being careful not to widen
them more than necessary . To remove carbon deposits
from the piston crown, use a slightly rounded
scraper . To clean the piston ring lands, use a discarded
piston ring, as shown in the illustration. Do not
use silicon carbide abrasive paper on the piston crown
or the lands. This will remove too much metal, and
cause pieces of silicon carbide to be embedded in the
piston which will quickly destroy the cylinder bore and
cause corrosion of the piston.
Inspect the piston skirt carefully . If you see hard
carbon deposits, it is best to eliminate them by dipping
the entire piston in a proprietary cleaner such as
carburetor cleaner .
WARNING : Cleaners capable of removing hard
carbon are inevitably extremely hazardous to use.
Their vapors can cause serious illness, and contact
with the skin or eyes will cause immediate
serious injury. Always use appropriate protective
equipment, such as goggles, and gloves, and
follow scrupulously the instructions and warnings
on the container and package of the cleaner.
If, after cleaning, the piston shows slight scoring on
the skirts, this may be used by very light rubbing with
a very fine flat stone.
CAUTION
: Do not get carried away. You can
quickly ruin a perfectly serviceable piston by
removing scores on the piston skirt. The very
lightest rubbing is always sufficient. Never use a
file, silicon carbide abrasives, or any abrasive
coarser than 800 grit on a piston skirt.
ch. 3
Release 00 2000-01
MA50 - MY50
3-5
3